Conventionally, differential pressure sensors that use sensor diaphragms for outputting signals in accordance with pressure differences have been used as differential pressure sensors for industrial use. These differential pressure sensors are structured so as to guide the respective measurement pressures, which will act on high-pressure-side and low-pressure-side pressure bearing diaphragms, to one side face and the other side face of a sensor diaphragm, through a filling liquid as a pressure transmitting medium, so as to detect the deformation of the sensor diaphragm as, for example, a change in a resistance value of a strain resistance gauge, to convert this change in the resistance value into an electric signal, so as to be outputted to the outside.
This type of differential pressure sensor is used when measuring, for example, a liquid surface height through detecting a pressure difference between two locations, upper and lower, within a sealed tank for storing a fluid that is to be measured, such as a high-temperature reaction tower in an oil refining plant.
FIG. 3 is illustrates a schematic structure for a conventional differential pressure sensor. This differential pressure sensor 100 is structured through incorporating, in a meter body 2, a sensor chip 1 having a sensor diaphragm (not shown). The sensor diaphragm in the sensor chip 1 is made from silicon, glass, or the like, and a strain resistance gauge is formed on a surface of the diaphragm, which is formed in a thin plate shape. The meter body 2 is structured from a main unit portion 3, made out of metal, and a sensor portion 4, where a pair of barrier diaphragms (pressure bearing diaphragms) 5a and 5b, which are pressure bearing portions, is provided on a side face of the main unit portion 3, and the sensor chip 1 is provided within a sensor chamber 4a of the sensor portion 4.
In the meter body 2, the pressure sensor chip 1 that is provided within the sensor chamber 4a of the sensor portion 4 is connected to the barrier diaphragms 5a and 5b that are provided in the main unit portion 3 through respective pressure buffering chambers 7a and 7b, which are separated by a large-diameter center diaphragm 6, and pressure transmitting media 9a and 9b, such as silicone oil, or the like, are filled into connecting ducts 8a and 8b, which connect the sensor chip 1 to the barrier diaphragms 5a and 5b. 
Note that the pressure transmitting medium, such as the silicone oil, is required because it is necessary to separate the strain (pressure)-sensitive sensor diaphragm from the corrosion-resistant pressure bearing diaphragms, in order to prevent foreign materials within the measurement medium from becoming adhered to the sensor diaphragm, and to prevent corrosion of the sensor diaphragm.
In this differential pressure sensor 100, a measurement pressure P1 from a process is applied to the barrier diaphragm 5a, and a measurement pressure P2, from the process, is applied to the barrier diaphragm 5b, as in the operating state during proper operation that is illustrated schematically in FIG. 4(a). As a result, the barrier diaphragms 5a and 5b undergo dislocation, and the pressures P1 and P2 that are applied thereto are directed to the one face and the other face of the sensor diaphragm of the sensor chip 1, by the pressure transmitting media 9a and 9b, through pressure buffering chambers 7a and 7b that are divided by the center diaphragm 6. The result is that the sensor diaphragm of the sensor chip 1 undergoes dislocation in accordance with the pressure differential ΔP between the pressures P1 and P2 that are directed thereto.
In contrast, if, for example, an excessively large pressure Pover is applied to the barrier diaphragm 5b, then, as illustrated in FIG. 4(b), the barrier diaphragm 5b undergoes a large dislocation, and the center diaphragm 6 undergoes dislocation in accordance therewith so as to absorb the excessively large pressure Pover. Given this, the barrier diaphragm 5b bottoms out on the bottom face (an excessive pressure guard face) of a recessed portion 10b of the meter body 2, controlling the dislocation thereof, and preventing the propagation of a greater differential pressure ΔP than that to the sensor diaphragm through the barrier diaphragm 5b. When an excessively large pressure Pover is applied to the barrier diaphragm 5a as well, as with the case wherein an excessively large pressure Pover is applied to the barrier diaphragm 5b, the barrier diaphragm 5a bottoms out on the bottom face (an excessive pressure guard face) of a recessed portion 10a of the meter body 2, controlling the dislocation thereof, and preventing the propagation of a greater differential pressure ΔP than that to the sensor diaphragm through the barrier diaphragm 5a. The result is that breakage of the sensor chip 1, that is, breakage of the sensor diaphragm in the sensor chip 1, due to the application of an excessively large pressure Pover is prevented in advance.
In this differential pressure sensor 100, the sensor chip 1 is enclosed within the meter body 2, thus making it possible to protect the sensor chip 1 from the outside corrosive environment, such as the process fluid. However, because the structure is one wherein the center diaphragm 6 and the recessed portions 10a and 10b are provided for controlling the dislocation of the barrier diaphragms 5a and 5b to protect the sensor chip 1 from excessively large pressures Pover thereby, the dimensions thereof unavoidably must be increased.
Given this, there has been a proposal for a structure for preventing breakage/rupture of the sensor diaphragm through preventing excessive dislocation of the sensor diaphragm, when an excessively large pressure is applied, through the provision of a first stopper member and a second stopper member in the sensor chip, and having recessed portions of the first stopper member and the second stopper member face the one face side and the other face side of the sensor diaphragm. See, for example, Japanese Unexamined Patent Application Publication No. 2005-69736 (“the JP '736”).
FIG. 5 illustrates schematically a sensor chip that uses the structure illustrated in the JP '736. In this figure: 11-1 is a sensor diaphragm; 11-2 and 11-3 are first and second stopper members that are bonded with the sensor diaphragm 11-1 interposed therebetween; and 11-4 and 11-5 are pedestals to which the stopper members 11-2 and 11-3 are bonded. The stopper members 11-2 and 11-3 and the pedestals 11-4 and 11-5 are structured from silicon, glass, or the like.
In this sensor chip 11, recessed portions 11-2a and 11-3a are formed in the stopper members 11-2 and 11-3, where the recessed portion 11-2a of the stopper member 11-2 faces the one face of the sensor diaphragm 11-1, and the recessed portion 11-3a of the stopper member 11-3 faces the other face of the sensor diaphragm 11-1. The recessed portions 11-2a and 11-3a have surfaces that are curved along the dislocation of the sensor diaphragm 11-1, where pressure guiding holes 11-2b and 11-3b are formed at the apex portions thereof. Pressure introducing holes (pressure guiding holes) 11-4a and 11-5a are formed in the pedestals 11-4 and 11-5 as well, at positions corresponding to those of the pressure guiding holes 11-2b and 11-3b of the stopper members 11-2 and 11-3.
When such a sensor chip 11 is used, then when there is a displacement of the sensor diaphragm 11-1 when an excessively large pressure is applied to the one face of the sensor diaphragm 11-1, the entirety of the dislocated face is supported and stopped by the curved surface of the recessed portion 11-3a of the stopper member 11-3. Moreover, then when there is a displacement of the sensor diaphragm 11-1 when an excessively large pressure is applied to the other face of the sensor diaphragm 11-1, the entirety of the dislocated face is supported and stopped by the curved surface of the recessed portion 11-2a of the stopper member 11-2.
This effectively prevents accidental rupturing of the sensor diaphragm 11-1 due to the application of an excessively large pressure, through preventing excessive dislocation when an excessively large pressure is applied to the sensor diaphragm 11-1, thus enabling an increase in the excessively large pressure guard operating pressure (withstand pressure). Moreover, in the structure illustrated in FIG. 3, the center diaphragm 6 and the pressure buffering chambers 7a and 7b are eliminated, and the measurement pressures P1 and P2 are guided directly from the barrier diaphragms 5a and 5b the sensor diaphragm 11-1, thus making it possible to achieve a reduction in the size of the meter body 2.
In a structure by which to achieve a reduction in size of this meter body 2, the sensor chip 11, as illustrated in FIG. 6, is contained within a sensor chamber 4a and is secured through bonding a pedestal 11-5 to the bottom face (wall face) 4b of the sensor chamber 4a. In this case, the measurement pressures P1 and P2 are applied, and the sensor diaphragm 11-1 flexes to the low-pressure side depending on the differential pressure ΔP between the measurement pressures P1 and P2. This flexing preferably is toward the bonded portion with the wall face 4b of the sensor chamber 4a of the sensor chip 11. If flexing were produced in the opposite direction, then the sensor chip 11 might delaminate from the bonded portion with the wall face 4b of the sensor chamber 4a. The bonded portion is pressed with a force F1 that depends on the product (S·P1) of the measurement pressure P1 and the surface area S that is formed by the outer periphery of the bonded portion of the wall face 4b and the sensor chamber 4a. On the other hand, the bonded portion is pulled apart by a force F2 in accordance with the product (X·P2) of the measurement pressure P2 and the non-bonded surface area X that is in communication with the measurement pressure P2 and that is surrounded by the bonded portion that is bonded to the wall face 4b of the sensor chamber 4a. If the sum of F1 and the force F3 with which the bonded portion is supported by the bond alone is not greater than F2, then the bond will delaminate. If the surface area S is, in the deformation thereof, greater than the surface area X, and P1 is greater than P2, then there will be no delamination. Moreover, the same relationship exists for, for example, the bonded portion for the stopper member 11-3 with the sensor diaphragm 11-1 within the sensor chip 11. Because of this, normally the side that bears the pressure P1 is used as the high-pressure side and the side that bears the pressure P2 is used as the low-pressure side.
However, in such a structure for the sensor chip 11, it is not possible to prevent delamination of the bonded portion of the sensor chip 11 (the bonded portion of the sensor chip 11 bonded to the wall face 4b of the sensor chamber 4a, or the bonded portions of the multilayer structure within the sensor chip 11) by simply establishing a high-pressure side and a low-pressure side if there is the possibility that the high/low relationship between the pressure P1 and the pressure P2 could become reversed or, even if the high/low relationship between the pressure P1 and the pressure P2 is not reversed, the pressure P1 side is selected as the low-pressure side and the pressure P2 side is selected as the high-pressure side through a technician error when installing the differential pressure sensor in the workplace.
The present invention is to solve such a problem, and an aspect thereof is to provide a differential pressure sensor able to prevent delamination of the bonded portion of the sensor chip.